This proposal requests support for ten predoctoral trainees in the field of molecular biophysics, drawn principally from the interdepartmental Graduate Group in Biophysics, and the Departments of Chemistry and Molecular and Cell Biology. The 26 training faculty are drawn from the foregoing and from the Departments of Physics, Bioengineering, Chemical and Biomolecular Engineering, and Plant and Microbial Biology. Our faculty are world leaders in their fields and include five members of the National Academy of Sciences, five Howard Hughes Medical Institute Investigators, and a recent recipient of the Breakthrough Prize in Life Sciences. The Molecular Biophysics Training Grant is the only training program at UC Berkeley focussing on molecular biophysics and the only training grant that supports graduate training within the Graduate Group in Biophysics. The goal of the program is to train future leaders in the application of the most powerful physics-based technologies and concepts to the most intractable, medically, and societally important problems. We have a sustained track record of producing graduates who have become leaders in academia, industry, and government research laboratories. We accomplish this with an integrated program whose four pillars are 1) three laboratory rotations in the first year, followed by mentored research in the second year and beyond; 2) core coursework in biophysical modeling and physical biochemistry; 3) career development through monthly lunch meetings, networking with internal and external speakers, an annual retreat, and trainee conference attendance; 4) training in ethical conduct and scientific integrity, rigor, and reproducibility.